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5/25/2014 6:38 P.M. ET

Top prospect Butler tosses seven scoreless

Right-hander working on string of 22 2/3 innings without earned run

Right-hander Eddie Butler, the Rockies' No. 2 prospect, threw seven scoreless innings Sunday and Double-A Tulsa defeated Midland, 2-1.

Butler, ranked No. 34 on MLBPipeline.com's Top 100 Prospects list, scattered five hits and didn't allow a runner to advance past second base. He struck out three, walked one and threw 93 pitches.

Butler hasn't allowed an earned run in 22 2/3 innings. The only blemish during the streak, which dates back to May 6, was an unearned run in his previous start.

Butler whiffed 143 batters in 149 2/3 innings across three levels last season, but he has seen his strikeout rate drop this season, fanning 36 over 64 frames for an average of 5.1 per nine innings, down from 8.6 last year.

But he is working more efficiently. He leads the Texas League in innings pitched and averages more than six innings per start. He has cut his walk rate from 3.1 per nine innings last season to 2.4 this year and his 2.39 ERA is the third best in the circuit.

Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.